[TowerTalk] More comments on lightning

M.G. Brafford wrote:
>
> FINALLY!!! A guy who knows what he is talking about!! Good job Dave!
>
> My towers, TV ants, trees etc etc etc etc etc have been HIT MANY times. I
> have drawn the same conclusion, ie lightning hits anywhere it pleases!
I heard firsthand a story about a ham who had all his computers and ham
equipment on a long table in the center of the room. When not in use,
all cords, connections, etc, were rolled up on top of the table. When
not in use there was six feet of open space in any direction in the
room.
He lived on a geographically high hill, which took a large number of
hits every year. One day, lightning hit the power pole out at the end of
the property. It got on to the phone line, vaporizing it, and all
attached, in the process, and jumped from the wall of the computer/ham
room to the table, ruining most of the equipment on top, and sent a
fireball rolling into the hall which chased the terrified wife out the
front door, scorching various spots on the way.
This IS consistent with the reports of fire jumping insulators on guy
lines, and ungrounded conductors serving as conduit for unsatisfied
lightning. It also is very discouraging. (Note that telco gastube
protectors are not grounding. By the time a large capacity strike is
coming over the phone line, it is already too late. They only serve for
surge protection.)
The soil at the aforementioned spot was rocky, and I doubt the ground
rod at the pole was an effective sink. Once the strike was in full
stride, there was a lot more to dissipate than the local ground could
absorb. OK, says the unsatisfied charge, let's see what we can do at the
end of this telephone line.
Keeping that thought, consider one very well done documentary that
featured high speed photography of a lightning strike forming. It showed
the leader forming from a 20' tree next to a barn with all the lightning
rod stuff on it, next to a power pole, presumably with all the usual
power pole ground stuff, GOING UP about 30 feet whereupon it flashed and
the strike blew up some number of branches in the tree.
When I was K4VDL in Virginia in the 60's, I had a 70' tower in my
backyard with a 40 meter vertical on top (kept grounded unless
operating). 100+ feet at top. It was never struck. However, lightning
did blow a 15 foot mimosa tree into toothpicks between mine and the
neighbor's house, a scant 65 feet away from the base of the tower.
It bothers me a bit to see some on this server discount anecdotal
material. If the theory cannot absorb the anecdotal material (assuming
no bald-faced lies), then the theory is short. On the other hand,
extrapolating a few anecdotes into a pet theory is equally short. But
MASSIVE anecdotal evidence cannot be ignored for it's practical uses:
Lightning rods work (eg, protect the barn) if connected to good grounds.
Massive ground fields under towers work.
Lightning LOVES trees.
Ungrounded or poorly grounded conductors from the vicinity of poorly
grounded lightning attractors create fireballs in the hall and burn down
people's houses (many years of fire dept. experience to back this up).
Here, simply disconnecting lines may guard against induced surge, but
may provide a path toward the house for a nearby strike on a tower with
a poorly dissipating ground system. Even grounding both ends would not
help if the connected grounds were poor.
Moving toward massive evidence:
Lightning doesn't strike "porcupines". Any reasonable theory must
explain why.
I'm putting up a tower shortly. I intend to put in a large ground system
as soon as the base is poured. What I don't know is how to measure the
lightning receptivity of the ground. Any help on this?
I'm following this thread with great interest. Some posts have bordered
on incivility. That's sad.
73 y'all, and may you never be chased by a fireball.
Guy.
-------
Guy L. Olinger
k2av@qsl.net
Apex, NC, USA
--
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm